Page No 257:

Question 1:

Why are
some substances biodegradable and some non-biodegradable?

Answer:

Some substances such as
metal, glass, plastic, etc. which cannot be decomposed by the living
organisms are non-biodegradable wastes. These substances are
non-biodegradable because the micro-organisms do not have enzymes
that can digest these substances. Therefore, we classify them as
non-biodegradable wastes. Other substances such as paper, vegetable
wastes, etc. that can be easily broken down by enzymes are
biodegradable wastes.

Page No 257:

Question 2:

Give any
two ways in which biodegradable substances would affect the
environment.

Answer:

Biodegradable
substances affect the environment in the following ways:

(i) The biodegradable
substances such as tree leaves, plant parts, and kitchen wastes can
be used as humus after composting. This will enhance the soil
fertility.

(ii) The biodegradable substances mainly contain
carbon. These substances after decomposition release that carbon back
into the atmosphere.

Page No 257:

Question 3:

Give any
two ways in which non-biodegradable substances would affect the
environment.

Answer:

Non-biodegradable
substances affect the environment in the following ways:

(i) They contaminate
soil and water resources as they cannot be decomposed by
micro-organisms.

(ii) These substances, when accidentally eaten by
stray animals, can harm them and can even cause their death.

Page No 261:

Question 1:

What are
trophic levels? Give an example of a food chain and state the
different trophic levels in it.

Answer:

A
trophic level is the level of species in an
ecosystem on the basis of the source of nutrition
such as producers, primary consumers, secondary consumers, etc.

The
producers form the first trophic level as they manufacture food. The
primary consumers form the second trophic level, the secondary
consumers form the third, and the tertiary consumers form the fourth
trophic level.

Trophic
levels:

Various
trophic levels are connected through food chains. For example, in an
aquatic food chain, phytoplanktons are the producers, zooplanktons
are the primary consumers, and small fish is the secondary consumer
and so on.

Aquatic food chain

Page No 261:

Question 2:

What is
the role of decomposers in the ecosystem?

Answer:

Decomposers
include micro-organisms such as bacteria and fungi that obtain
nutrients by breaking down the remains of dead plants and animals.
They help in the breakdown of organic matter or biomass from the body
of dead plants and animals into simple inorganic raw materials, such
as CO2,
H2O,
and some nutrients.

Page No 264:

Question 1:

Which of
the following groups contain only biodegradable items?

(a) Grass,
flowers and leather

(b) Grass,
wood and plastic

(c) Fruit-peels,
cake and lime-juice

(d) Cake,
wood and grass

Answer:

(c)Fruit-peels,
cake, and lime-juice

(d)Cake,
wood, and grass

Page No 264:

Question 2:

Which of
the following constitute a food-chain?

(a) Grass,
wheat and mango

(b) Grass,
goat and human

(c) Goat,
cow and elephant

(d) Grass,
fish and goat

Answer:

(b) Grass,
goat, and human

Page No 264:

Question 3:

Which of
the following are environment-friendly practices?

(a) Carrying
cloth-bags to put purchases in while shopping

(b) Switching
off unnecessary lights and fans

(c) Walking to school instead of getting your mother to drop you on
her scooter

(d) All of
the above

Answer:

(d) All
of the above

Page No 265:

Question 4:

What will happen if we kill all the organisms in one trophic level?

Answer:

Various
trophic levels are connected through the food chains. If all the
organisms of any one trophic level are killed, then it will disrupt
the entire food chain.

For
example, in a food chain, if all the plants are killed, then all the
deer will die due to lack of food. If all the deer are dead, then
soon the tigers will also die. Due to the death of these animals, the
decomposer’s population will rise in that area.

This
is just an example of one food chain. However, in nature, food chains
are not isolated. They are interconnected in the form of food web.
Therefore, killing all the plants of an area will not only affect the
deer, it will also affect other herbivores such as goat, cattle,
sheep, etc.

Page No 265:

Question 5:

Will the
impact of removing all the organisms in a trophic level be different
for different trophic levels? Can the organisms of any trophic level
be removed without causing any damage to the ecosystem?

Answer:

Organisms
of all trophic levels are equally important and are an integral part
of the ecosystem. If all the producers are removed, then it will
affect all the herbivores as it is their primary food source. Death
of herbivores will soon affect the primary carnivores and so on.

Now let us
suppose that all the deer (herbivores) are killed in a region. This
can lead to an increase in the number of producers. At the same time,
there will be an increase in the number of other herbivores such as
rabbits, goat, sheep, etc. due to less competition. This will also
lead to the increase in population of only consumers of these
increased herbivores. Thus, the balance in the ecosystem gets
disturbed if any of its component organisms are removed.

Page No 265:

Question 6:

What is
biological magnification? Will the levels of this magnification be
different at different levels of the ecosystem?

Answer:

Biomagnification
is the increase in the concentration of pollutants or harmful
chemicals within each step of the food chain. The levels of
biomagnification will be different at different trophic levels. For
example, in a pond of water, DDT was sprayed and the producers were
found to have 0.04 ppm concentration of DDT. Since many types of
planktons are eaten by some fishes and clams, their body accumulates
0.23 ppm of DDT. Sea gull that feeds on clams accumulates more DDT as
one sea gull eats many clams. Hawk, the top carnivore, has the
highest concentration of DDT.

Biomagnification

Page No 265:

Question 7:

What are
the problems caused by the non-biodegradable wastes that we generate?

Answer:

Non-biodegradable
substances affect the environment in the following ways:

(i) Since the non-biodegradable substances cannot be broken down,
they get accumulated and thus contaminate the soil and the water
resources.

(ii) These substances, when accidentally eaten by some stray animal,
can harm them and can even cause their death.

(iii) These substances occupy more space in the
landfills and require special disposal
techniques.

(iv) These materials can accumulate in the
environment and can also enter the food
chain.

Page No 265:

Question 8:

If all the
waste we generate is biodegradable, will this have no impact on the
environment?

Answer:

Generation
of only biodegradable waste will have a positive impact on the
environment. There will not be any pollution caused by the
non-biodegradable wastes. The problem associated with waste
management and disposal will also not occur. The population of
decomposers will increase to breakdown the extra biodegradable waste
generated.

Page No 265:

Question 9:

Why is
damage to the ozone layer a cause for concern? What steps are being
taken to limit this damage?

Answer:

Ozone
depletion occurs widely in the stratosphere. However, it is more
prominent over the Antarctic region and is known as the ozone hole.

It
can result in the death of many phytoplanktons that leads to
increased global warming.

To limit the damage to
the ozone layer, the release of CFCs into the atmosphere must be
reduced. CFCs used as refrigerants and in fire extinguishers should
be replaced with environmentally-safe alternatives. Also, the release
of CFCs through industrial activities should be controlled.